Conventionally, Japanese Patent Application JP 2007-245982 A teaches a tire air pressure monitoring device for determining on which wheel a transmitter of a tire pressure sensor installed on a tire of each wheel is positioned.
During a vehicle running, the transmitter rotates together with the wheel and the difference may occur in the rotation speeds among the respective wheels. Therefore, in order to accurately determine the wheel position of the transmitter, it is preferable to accurately detect a rotational position (rotational angle) at which the transmitter of each wheel performs transmission on a side of vehicle body. However, if the rotational position information of the wheel detected by the vehicle body side is input sporadically at a predetermined time interval, it may be difficult to detect the rotational position accurately on the vehicle body side with a possibility of deterioration in the detection accuracy of the transmitter. An object of the present invention is to provide a tire pressure monitoring device that can determine more precisely the wheel position of the transmitter.